Intensification electrode assembly for developer in office photocopy machine

ABSTRACT

An electrode assembly for use in an office photocopy machine of the type in which a copy sheet carrying a latent image made up of electrostatic charges is guided into a developer tray having a developer liquid in the form of a colloidal suspension of toner particles in a dielectric vehicle. The electrode has a cylindrical face formed into ridges and appearing, in transverse section, to be of sawtooth configuration. The electrode is submerged in the developer liquid closely adjacent the copy sheet. Means are provided for preventing initial contact between the electrode and the leading edge of the copy sheet.

United States Patent Renter, Jr. et a1.

1451 Jan. 25, 1972 [54] INTENSIFICATION ELECTRODE ASSEMBLY FOR DEVELOPER IN OFFICE PHOTOCOPY MACHINE [73] Assignee: American Photocopy Equipment Company, Evanston, Ill.

[22] Filed: Aug. 31, 1970 [211 App]. No.: 68,355

52 user ..ll8/637,ll7/37 511 1111.01. ..G03g 13 00 581 Field of Search ..1 18/637 1.x;117/37 1.x,17.5;

[56] References Cited UNITED STATES PATENTS 3,249,088 5/1966 Ostensen ..l18/637 Primary ExaminerMervin Stein Assistant Examiner-Leo Millstein Attorney-Wolfe, Hubbard, Leydig, Voit & Osann, Ltd.

[57] ABSTRACT An electrode assembly for use in an office photocopy machine of the type in which a copy sheet carrying a latent image made up of electrostatic charges is guided into a developer tray having a developer liquid in the form of a colloidal suspension of toner particles in a dielectric vehicle. The electrode has a cylindrical face formed into ridges and appearing, in transverse section, to be of sawtooth configuration. The electrode is submerged in the developer liquid closely adjacent the copy sheet. Means are provided for preventing initial contact between the electrode and the leading edge of the copy sheet.

5 Claims, 6 Drawing Figures INTENSIFICATION ELECTRODE ASSEMBLY FOR DEVELOPER IN OFFICE PIIO'IOCOPY MACHINE It is known to provide an intensification electrode opposite the face of an electrostatic copy sheet immersed in a developer liquid of the colloidal type. The purpose of such intensification electrode is to serve as an opposite pole for the regions of electrostatic charge on the sheet which results in the intensification of the electrostatic field, avoidance of fringing" effect, and orientation of the lines of electrostatic flux more nearly perpendicular to the surface of the sheet. In a practical case, where zinc oxide is used in a binder to hold the charge, the toner particles tend to follow the electrostatic lines of flux into contact with the surface of the sheet, where deposition occurs in proportion to the amount of charge. While it has been proposed to apply biasing potentials to the intensification electrode, it is generally preferred to have such electrode electrically floating.

It is an object of the present invention to provide an intensification electrode which operates more efficiently than electrodes which have been heretofore available and which is capable of being closely spaced, or coupled, to the face of the photocopy sheet for maximum intensification of the electrostatic field while at the same time providing constant replenishment of the developer liquid in the restricted spaces so that the black areas are assured of adequate pigmentation and so that starvation" of such areas, experienced in some developer designs, is avoided. Thus it is an object to take care of the conflicting requirements of close spacing, on the one hand, and maintenance of high toner density in the developer liquid, on the other, in the regions of close spacing.

It is a related object to provide an intensification electrode which does not require positive pumping of the developer liquid in the region of development but in which there is, nevertheless, circulation of the developer liquid both peripherally and axially with respect to the surface of the electrode. Consistent and uniform development over the entire sheet is assured, free of the harmful effects of localized turbulence which have accompanied past efforts to pump developer liquid into the confined spaces where development primarily takes place.

It is another object of the present invention to provide an intensification electrode assembly which results in complete development within an extremely short period of time and which is therefore well suited for use with photocopy machines having a high production rate.

It is a specific object of the present invention to provide an intensification electrode having ridges of sawtooth cross section defining grooves for automatic replenishment, each groove forming a local reservoir for the liquid to make available toner particles in sufficient density to produce full and prompt development. The sawtooth cross section not only facilitates peripheral circulation but precludes any possibility of a copy sheet becoming hung up" during the course of development.

It is a more specific object to provide an intensification electrode assembly which permits extremely close spacing between the electrode and face of the sheet while insuring against direct brushing contact between the electrode and the sheet, particularly as the leading edge of the sheet is first moved into developing position adjacent the electrode.

It is yet another object of the invention to provide an intensification electrode which may be utilized in machines of conventional design without any substantial modification or expense.

Other objects and advantages of the invention will become apparent upon reading the attached detailed description and upon reference to the drawing in which:

FIG. 1 is a cross-sectional view taken through an electrostatic developer unit employing toner in colloidal suspension;

FIG. 1a is a diagrammatic and fragmentary section taken along the line 1a1a in FIG. 1;

FIG. 2 is an enlarged fragmentary section taken along the line 22 in FIG. 1;

FIG. 3 is an enlarged fragmentary section showing the sawtooth configuration of the intensification electrode;

FIG. 4 is a diagram at an enlarged scale taken along line 4- 4 in FIG. 3 showing the orientation of the lines ofelectrostatic flux which determines the path followed by the toner particles; and

FIG. 5 is an enlarged fragment based upon FIG, 1 and showing control of the leading edge of the copy sheet at the entryway.

While the invention has been described in connection with the preferred embodiment, it will be understood that we do not intend to be limited to the particular embodiment shown but intend, on the contrary, to cover the various alternative and equivalent constructions included within the spirit and scope of the appended claims.

Turning now to the drawing there is disclosed in FIG. I, in vertical section, a typical developer unit 10 having a base 11 and superimposed tray 12 which fit together and both of which may be molded of plastic. The tray is of generally cylindrical contour, having guides in the form of a plurality of axially spaced ribs 13 which are smoothly surfaced and molded integrally and which together define a cylindrical guide surface 14 (see FIG. 4) having an entryway 15 at one end and an exit 16 at the other.

The tray has a charge 20 of developer liquid which, during operation of the machine, is pumped from a lower compartment indicated at 21 via a line 22 for discharge at an orifice 23. Drain openings, not shown, at the ends of the tray permit the excess developer liquid to drain back down into the storage space 21. For purpose of the present invention the tray may simply be assumed to have a charge of developer liquid maintained at approximately the indicated level.

For transporting a copy sheet, indicated at 30, through the developer tray, a pair of inlet rollers 31 are provided driven by a motor M and horizontally arranged so that the outlet nip feeds the copy sheet 30 downwardly into engagement with the guide surface 14 within the tray. Under normal circumstances the copy sheet, because of its normal and inherent stiffness, tends to follow a path of maximum diameter so that it maintains contact with the guide surface 14 until the exit 16 is reached. At this point the copy sheet is engaged by a pair of rotating expeller rollers 32 driven at substantially the same peripheral speed by the motor M and at least one of which is resiliently surfaced so as to squeegee the excess developer liquid into the apron portion 33 of the tray. From the expeller rollers the copy sheet, in practically dry condition, is subjected to a flow of warmed air and discharged into suitable collector tray.

In accordance with the present invention a metallic intensification electrode is provided submerged in the developer liquid and having a generally cylindrical surface which extends parallel to the copy sheet guide surface 14, the electrode surface being formed with longitudinally extending ridges closely coupled to the copy sheet and having a sawtooth profile defining open-ended grooves which serve as reservoirs of developer liquid immediately adjacent the closely coupled regions for complete and prompt development of the charged areas. Further in accordance with the invention the sloping sides of the ridges are faced toward the entryway to facilitate flow of the developer liquid from the grooves upon passage of the copy sheet and to insure free movement of the copy sheet through the developer unit without any possibility that the leading edge of the copy sheet may be obstructed by, or become hung up upon, one of the ridges. Referring to the drawing, the metallic intensification electrode, generally indicated at 40, has a cylindrical portion 41 and a flat horizontal portion 42 and may be conveniently formed as a D-shaped extrusion of aluminum or the like.

lntegrally formed on the cylindrical outer surface of the electrode are a plurality of ridges 43 which extend the length of the electrode and beyond the lateral edges of the copy sheet. Each ridge has a crown 44, a sloping surface 45 which extends in the direction of the entryway, and an abrupt, inwardly extending surface 46. Thus the surfaces of adjacent ridges define grooves 47 which are occupied by developer liquid and which serve as local reservoirs for furnishing developer liquid to the restricted or close-coupled regions 48 at the crowns of each of the ridges. The spacing in the regions ofclosest approach, indicated at 48, is preferably on the order of 0.050 inch. Assuming that a typical copy sheet having a thickness of 0.004 inch is used, this leaves a net spacing between the crowns of the ridges and the surface of the copy sheet on the order of0.046 inch.

in order to understand the mechanism of development, reference is made to FIG. 4 which shows, in greatly enlarged form, a small section of copy sheet 30 having a sensitive layer 30a, formed of particles of zinc oxide in a dielectric binder, with a paper backing indicated at 30b. As a result of the preceding steps of charging and exposure, the copy sheet will have a latent image in the form of negatively charged areas such as that indicated at 50. The negatively charged region of the copy sheet will tend to induce a positive charge 51 in the portion of the intensification electrode which is directly op posite. This creates lines of electrostatic flux indicated at 52 which extend generally perpendicularly to the face of the copy sheet and which represent a force field capable of acting upon positively charged toner particles, such as indicated at 53, which are colloidally suspended in the liquid vehicle. The vehicle may consist of petroleum distillate, Freon, or other thin dielectric liquid capable of reasonably rapid evaporation as the copy sheet leaves the developer unit. The positively charged toner particles are attracted to the surface 300 along the lines of flux to pigment the charged areas and tending to neutralize the charge. Most of the development occurs in the region of the first few ridges. Passage of the sheet opposite the additional ridges provides additional opportunity for deposition of the toner so that the black areas are quickly and completely saturated.

In addition to the multiple and successive regions of intensification provided by the electrode, it may be noted that the sawtooth configuration, with the sloping surfaces facing toward the entryway, facilitates the drawing of fresh developer liquid into the close-coupled regions by reason of movement of the copy sheet. Thus, as indicated by the arrows in FIG. 3, movement of the sheet 30 tends to draw fresh liquid from the grooves 47 which act as local reservoirs for toner. Moreover it will be apparent to one skilled in the art that in the event that a copy sheet enters the developer having a leading edge which tends to curl in the direction of the intensification electrode, the sloping surfaces 45 on each of the ridges will tend to shed the leading edge thereby preventing any possibility of hang-up" and resultantjamming in the developer unit.

in addition to the peripheral flow of the liquid in the direction of the arrows in FIG. 3, it will be understood that the ends of the grooves 47 are open to the body of liquid at each end so that there will be naturally occuring flow of replenishing liquid inwardly from the ends. A further source of replenishment resides in the fact that a sheet 30 does not occupy an obstructing position at all times and, between successive sheets, there is a direct connection between the liquid in the grooves 47 and the liquid occupying the space between the adjacent ribs 13, with circulation between the two, which assists in maintaining toner concentration at a high level.

The multiple regions of field intensification about the periphery of the electrode and the continuous replenishment of liquidborne toner in such regions has resulted in a permissible increase in the speed of development by a factor of almost two as compared to prior constructions. It is found that complete development can be secured at a sheet transport speed in excess of 6 inches per second in a developer tray of limited size where the total passage through the body of developer liquid is only on the order of4 to inches. This assumes, of course, that means are provided for constantly adding additional toner to the vehicle as it is fed into the developer tray in order to maintain the incoming developer liquid at a constant toner concentration. Means for adding additional toner from time to time under automatic control may, for example, be found in Sacre US. Pat. No. 3,368,525 which issued on Feb. 13, l968.

It is one of the features of the present construction that an insulated guide is provided at the entryway of the tray extending along the length of the electrode and in a slightly overhanging position so that the leading edge of the sheet is guided into engagement with the tray guide surface, preventing direct contact between the face of the sheet and the initial ridge or ridges of the intensification electrode. Thus, referring to FIGS. l and 5, the developer assembly is provided with a top member 60, which may be molded of plastic or other insulating material, and which has a surface 61 at the leading edge which slightly overhangs the first of the ridges 43 of the electrode. in the event that the sheet 3!) does not proceed straight downwardly from the inlet rollers 31 but tends to feed in an angled position as shown in FIG. 5, the leading edge of the sheet, striking the surface 61, is directed laterally into contact with the guide surface l4. Once the sheet is wetted and in con tact with the guide surface, experience shows that it tends to remain in contact with such surface during the entire course of travel until it exits from the developer unit. Use of the insulated guide therefore completely avoids the effect, sometimes experienced, of streaks or other irregularities resulting from electrode contact at the leading edge. Discharge of incoming liquid through the horizontally extending lip opening s2 under the surface fill assists in maintaining the incoming sheet seated against the guide surface 14.

It is one of the features of the present construction that it is not limited to use in new designs of developer units. Since most developer trays guide the sheet about a cylindrical path, the electrode may be added to older designs of developer trays thereby achieving the results of the invention, including an increase in reliability and the crispness and density of the resulting copies, at minimum cost.

We claim as our invention:

ll. In a developer assembly for an electrostatic type office photocopy machine, the combination comprising a tray hav ing an entryway and an exit with internal guides extending therebetween for guiding a charged copy sheet face up about a generally cylindrical path, the tray having a charge of toner particles colloidally suspended in a thin insulating vehicle, a metallic intensifier electrode having a cylindrical surface extending in parallel relationship to the copy sheet guide means, the surface of the electrode being formed with longitudinally extending ridges having crowns extending into close-coupled relation to the copy sheet and defining between them openended grooves which serve as reservoirs of developer liquid immediately adjacent the closely coupled regions for continuous replenishment of the toner particles therein, the ridges in cross section having a sawtooth profile with the sloping sides of the ridges being faced toward the entryway.

2. The combination as claimed in claim 1 in which the individual teeth forming the sawtooth profile have a narrow crown with a sloping surface on one side and an abrupt inwardly extending surface on the other.

3. The combination as claimed in claim I in which the internal guide means is in the form of a plurality of smoothly surfaced peripherally extending ribs integrally formed on the inside surface of the tray.

4 The combination as claimed in claim l in which the intensification electrode is a hollow extrusion formed of aluminum or the like having a generally D-shaped cross section.

5. In a developer assembly for an electrostatic-type of office photocopy machine the combination comprising a tray having a generally cylindrical inner surface with an entryway along one side and an exit along the other, a pair of entry rollers at the entryway having a nip aligned therewith to direct the leading edge of the copy sheet against the cylindrical inner surface, the tray having a charge of toner particles colloidally suspended in a thin insulating vehicle, a metallic intensifier electrode having a cylindrical outer surface evenly spaced with respect to the inner surface of the tray, an insulator extending along the length of the intensification electrode at the entryway and slightly overhanging the same for intercepting the leading edge of the copy sheet and for deflecting it toward the inner surface of the tray thereby to prevent the leading edge portion of the copy sheet from directly engaging the adjacent portion of the metallic electrode, the surface of the electrode being formed with ridges along the length thereof and extending beyond the lateral edges of the copy sheet, said ridges in cross section being of sawtooth configuration having a crown extending into close-coupled relation to the surface of the copy sheet and having sloping sides faced in the direction 

1. In a developer assembly for an electrostatic type office photocopy machine, the combination comprising a tray having an entryway and an exit with internal guides extending therebetween for guiding a charged copy sheet face up about a generally cylindrical path, the tray having a charge of toner particles colloidally suspended in a thin insulating vehicle, a metallic intensifier electrode having a cylindrical surface extending in parallel relationship to the copy sheet guide means, the surface of the electrode being formed with longitudinally extending ridges having crowns extending into close-coupled relation to the copy sheet and defining between them open-ended grooves which serve as reservoirs of developer liquid immediately adjacent the closely coupled regions for continuous replenishment of the toner particles therein, the ridges in cross section having a sawtooth profile with the sloping sides of the ridges being faced toward the entryway.
 2. The combination as claimed in claim 1 in which the individual teeth forming the sawtooth profile have a narrow crown with a sloping surface on one side and an abrupt inwardly extending surface on the other.
 3. The combination as claimed in claim 1 in which the internal guide means is in the form of a plurality of smoothly surfaced peripherally extending ribs integrally formed on the inside surface of the tray.
 4. The combination as claimed in claim 1 in which the intensification electrode is a hollow extrusion formed of aluminum or the like having a generally D-shaped cross section.
 5. In a developer assembly for an electrostatic-type of office photocopy machine the combination comprising a tray having a generally cylindrical inner surface with an entryway along one side and an exit along the other, a pair of entry rollers at the entryway having a nip aligned therewith to direct the leading edge of the copy sheet against the cylindrical inner surface, the tray having a charge of toner particles colloidally suspended in a thin insulating vehicle, a metallic intensifier electrode having a cylindrical outer surface evenly spaced with respect to the inner surface of the tray, an insulator extending along the length of the intensification electrode at the entryway and slightly overhanging the same for intercepting the leading edge of the copy sheet and for deflecting it toward the inner surface of the tray thereby to prevent the leading edge portion of the copy sheet from directly engaging the adjacent portion of the metallic electrode, the surface of the electrode being formed with ridges along the length thereof and extending beyond the lateral edges of the copy sheet, said ridges in cross section being of sawtooth configuration having a crown extending into close-coupled relation to the surface of the copy sheet and having sloping sides faced in the direction of the entryway to define grooves for holding a reservoir of developer liquid which, upon movement of the copy sheet, tends to be drawn into the region of the crown for replenishment of the toner particles which have been attracted toward the copy sheet, and a pair of driven expeller rollers at the exit for engaging the copy sheet and for discharging it externally of the tray. 